Ten years ago, Russian oligarch Mikhail Khodorkovsky was arrested at gunpoint on board his private jet.

In the decade since he has gone from being Russia's richest man, to its most famous political prisoner.

From inside the prison camp where he is being held in the far north of the country, he agreed to answer Sky News' questions.

"Jail is a great leveller," he told us.

"I lost much when I came into jail, many people arrive having had so little, they barely notice the difference.

"It makes it equal in a funny sort of way."

Image Caption:Khodorkovsky in 2003 after being named chief executive of YukosSibneft Oil

We asked him to describe his daily life in Penal Colony No 7 - a prison camp in the remote Karelia region, notorious for its Stalin-era Gulag.

Speaking through his legal team, he replied: "We have an eight-hour working day, plus inspections, plus a little bit of time for reading, writing or meetings with lawyers.

"We are held in barracks with 100-150 people in a barrack; the sleeping quarters are two square metres per person; it is warm in the barrack, this is very important.

"Overnight it is quiet, the light remains on, and an inspector walks inside the facility once every two hours. But this does not bother me.

"Clothing is issued and laundered. There is a common toilet, but it is clean. I shower once a week.

"I can see traces of meat in the food regularly: fresh vegetables - sometimes in the prison shop.

"I receive a parcel once every two months from home: 20kg. I ask for nuts, dried fruits and coffee.

"After 10 years you get experienced looking after your health."

Once the country's most successful entrepreneur, Khodorkovsky was arrested in 2003 and subsequently convicted of tax evasion and fraud over the course of two high-profile trials.

He argues the charges are contradictory as he has effectively been convicted of both stealing almost all of the oil from his own Yukos Oil Company, whilst simultaneously failing to pay taxes on it.

But many believe his real crime was to cross President Vladimir Putin by venturing into Russian politics and daring to challenge him in public.

Amnesty International has designated Khodorkovsky a prisoner of conscience.

We asked him about the case of the 'Arctic 30' - the protesters and journalists detained on board a Greenpeace ship in the Russian Arctic last month.

He described it as the latest manifestation of a Kremlin tightening the screws.

He said: "At least in the short-term the protesters will be treated as the Russians, in the hope of deterring others. I think they will then be released.

"Vladimir Putin has indicated his position very clearly – he puts on the pressure and those who do not agree must resist the pressure.

"So if the Russian people are resigned to accepting his authority he tightens the screws. If they resist, he checks their strength, and where necessary unscrews.

"If foreigners have also resigned themselves to accepting this, why should he behave any other way?"

Asked about the future of Russia under Mr Putin, Khodorkovsky said the country was stagnating and losing stability - a path that could end once again in revolution.

He said: "The reasons for the stagnation are self-evident: an irremovable, out-of-control power is losing flexibility, getting old, and being destroyed by corruption.

"Personal and social advancement have come to a standstill for everyone except a narrow circle of insiders and exceptional sycophants.

"The country is losing stability in the face of the inevitable crises. The opposition, geared for evolutionary development, is gradually being displaced by radicals."

He outlined two possibilities - "top-down" reforms led by Mr Putin, or "bottom-up" reforms demanded by mass protest, triggered by a crisis.

He said: "The risk is that in the second case a shift into revolutionary mode is very likely, and in Russia this is fraught with the danger of a revival of authoritarianism, simply with other persons in charge."

Khodorkovsky turned 50 in prison earlier this year. He is due to be released in August 2014, but there are already rumours of a third case being prepared against him.

Asked about his prospects for release or further prosecution, he replied: "Over 10 years I have become convinced that in my case nothing is impossible."